Using empty keys results in a bigger, uglier dump, but allows a given hive to contain both a value and subhives. Please note that this is different behavior compared with earlier releases, in which empty keys were not used and it was not legal to have a value and a hive at a given path. It is possible, although fairly unlikely, that this format will change again. The Hash store should generally be used for testing things that use a hive, as opposed for building hashes that will be used for anything else.